Effect of oxygen partial pressure in deposition ambient on the properties of RF magnetron sputter deposited GdO thin films.

Gadolinium oxide is an excellent optical material that offers high transmission in a wide wavelength range of 200-1600 nm and exhibits a high bulk refractive index of ∼1.80 at 550 nm. In the present study, a set of GdO thin films has been deposited on fused silica substrates by RF sputtering of a GdO target under various O to Ar flow ratios. The samples have been characterized by grazing incidence x-ray diffraction (GIXRD) to study the long range structural behavior, by GIXR to study density and surface roughness of the films, by atomic force microscopy measurements to study morphological properties, by Rutherford backscattering measurements for compositional studies, and by transmission spectrophotometry and spectroscopic ellipsometry techniques to study their optical properties. It has been observed that the films deposited with 10% oxygen partial pressure have low density, high surface roughness, and high void content, which results in a low value of refractive index of this film, and film quality improves as oxygen partial pressure is further increased. Extended x-ray absorption fine structure measurement with synchrotron radiation has also been employed to extract local structural information around Gd sites, which has in turn been used to explain some of the observed macroscopic properties of the films.